A filter press comprising such filter plates is known, for example, from EP 0 540 705 B1. Here, the filling elements are formed as rod-shaped tube bodies laid in a sealing manner into a groove-shaped recess of the sealing edge, which recess extends at the edge in the direction of said sealing edge. A sealing edge extends between said recess and said filter chamber which sealing edge is provided with transversal openings arranged transversely to its extension and corresponding with pulp exit openings of the tube body. In this way, a flow connection is produced between the tube body and the filter chamber.
Such filling elements are especially advantageous if an endless filter tape extending in a zig-zag shape around the filter plates is to be used. It is, however, a disadvantage of this design that the filling elements penetrate the sealing edge of the filter chambers and thus may, especially in the case of high pressures, cause sealing problems. Furthermore, a separate supply line for the supply of suspension outside the filter plate package as well as a plurality of connection lines between the supply line and the filling elements are required. Finally, special provisions are to be made for supporting the filling elements arranged approximately in the center of the intermediate space between two filter plates after these have been spaced apart to their emptying distance.
An alternative way of supplying the suspension is a so-called central pulp inlet arranged in a central position within the plate face and formed by a number of passage openings in the filter plates corresponding with the number of individual filter plates. In the filtration position of the filter plate package, the passage openings are composed to form a central inlet channel sealed at the joining points from which channel the pulp can enter the individual filter chambers.
It is a disadvantage of this design that the effective filter area and the chamber volume are reduced by the passage bores in the filter plates and that in the case of deformations of the filter plates due to an uneven pressure exerted on them the inlet cross-sections of the individual chambers are altered which may cause even larger differences in the pressure level of adjacent chambers.
Furthermore, so called corner inlets are generally known as another type of feeding suspension. Here, the corner portions of the filter plates are provided with passage openings flush to each other which in a compressed state of the package form a pulp channel extending near the corners and arranged inside the sealing edge of the filter plate. It is an advantage compared to a central pulp inlet that the diaphragm movement is affected neither by supporting toes nor by the central diaphragm clamps in the inlet area. Also, the suspension feeding cross-section cannot change due to plate deformation which means a more even filling and a more even pressure generation than in the case of a central inlet.
It is a disadvantage of the corner inlet that the filter cloths have to be fixed to the filter plates by clamps, for example by means of screwable clamp rings in the inlet area. On the one hand, this means a comparatively high working effort when replacing the filter cloths. On the other hand, such a fixation of the filter cloths on the filter plate excludes the possibility of cleaning a filter cloth by means of a movable pair of rollers around which the filter cloth runs in an S-shaped manner. Such a possibility of filter cake removal is known from DE 195 46 701 A1 and DE 197 45 289 C1.